Select groups of premalignant oral lesions are associated with a high incidence of developing into oral squamous cell carcinoma (OSCC). Premalignant lesions with increased levels of dysplasia contain higher macrophage content. Since tumor-associated macrophages can facilitate tumor progression, we hypothesize that macrophages within premalignant oral lesions can also promote motility and invasiveness of premalignant lesion cells. Our pilot studies showed that upon exposure to premalignant lesion cells, macrophages acquire the capacity to stimulate the motility and invasiveness of premalignant lesion cells. This stimulation of motility is primarily mediated through macrophage production of TGF-[unreadable]1. TGF-[unreadable]1, in turn, diminishes the activity of the serine/threonine protein phosphatase, PP-2A, and levels of its activator, ceramide. Diminished PP-2A activity is alone sufficient to activate motility-stimulatory pathways. Pilot studies with keratinocytes, premalignant lesion cells and tumor cells have shown that inhibition of PP-2A stimulates motility through pathways that require serine phosphorylation of paxillin and its dissociation from FAK/Src/paxillin focal adhesion complexes. Also required in the stimulated motility of PP-2A-inhibited cells is activation of Src, inactivation of the PI3K signaling antagonist PTEN, and PI3K activity. The hypothesis of this study is that macrophage-derived TGF-[unreadable]1 drives premalignant lesion cells toward invasiveness and that interrupting the motility signaling pathways blocks progression toward malignancy. This hypothesis will be tested through the following specific aims: 1. To define how macrophage-derived TGF-[unreadable]1 triggers motility in premalignant lesion cells. 2. To demonstrate in vivo the role of macrophages in driving premalignant lesion cells toward invasiveness. Method: The proposed studies will define with patient samples and in carcinogen-induced premalignant lesion mouse models the role of macrophage-derived TGF-[unreadable]1 in stimulating invasiveness of premalignant lesion cells and if this is dependent on TGF-[unreadable]R/Smad signaling. Significance: These studies will define how macrophages contribute to the invasiveness of high-risk premalignant oral lesion cells. In addition, they will provide the foundation for new approaches by which to prevent OSCC in patients that have premalignant oral lesions having a high risk of progression to malignancy. PUBLIC HEALTH RELEVANCE: Oral squamous cell carcinoma is the 6th most common neoplasm in the world with a 5 year survival of less than 50%. The proposed studies have direct relevance to the goal of reducing oral cancer development from premalignant oral lesions.